The regulation of specific antibody synthesis by T lymphocytes which recognize idiotypic determinants on B lymphocytes will be studied. Subpopulations of idiotype related T helper and T suppressor cells will be isolated and examined for their ability to influence idiotype expression at the level of the antibody-forming cell. The interactions between carrier-specific and idiotype-specific T cells will be analyzed, and evidence for MHC restriction of idiotype-related T cell activity will be sought. The environment required for the induction of idiotype-related regulatory activity will be studied in normal and genetically-defective mice. Finally, the nature and number of receptors present on idiotype-related T cells will be evaluated using anti-receptor reagents and the fluorescence activated cell sorter.